This application is based on Patent Application No. 10-261887 filed in Japan, the content of which is hereby incorporated by reference.
1. Field of the Invention
The present invention relates to a solid immersion lens and production method thereof, and specifically relates to a solid immersion lens used as a recording/reading head for a high resolution microscope probe or high density optical memory (recording/reading) and production method thereof.
2. Description of the Related Art
In the field of optical memory for optically recording/reading information, the following two methods have been proposed in recent years for increasing the recording density of disks used as a recording media.
(1) Shorten the wavelength of the light used for recording/reading.
(2) Increase the aperture number NA of the object lens converging the light on the disk.
Among these methods, method (1) requires the development of a semiconductor laser or the like for emitting light of a shorter wavelength to reduce the wavelength of the light itself. The development of such a semiconductor laser is not yet a simple matter, however.
Focusing on method (2), there have been various proposals for emitting the light used for recording/reading on a disk using a solid immersion lens. This method is based on the principle of the liquid immersion microscope (i.e., improved resolution microscope via liquid immersion method). That is, this method utilizes the principle of the microscope obtaining a resolution at less than 100 nm in visible light. Prior applications of related art include U.S. Pat. Nos. 5,004,307 and 5,764,613.
Solid immersion lenses heretofore experimentally produced include the hemispherical solid immersion lens 41 shown in FIG. 14, and the hyperhemispherical solid immersion lens 42 having a cap piece remaining under the hemisphere as shown in FIG. 15. In FIGS. 14 and 15, reference number 43 refers to a normal objective (condenser) lens, and reference number 44 refers to a recording medium (disk).
In the hemispherical solid immersion lens 41, the light beam LB enters perpendicular to the concave surface 41a, and is converged by the plane surface 41b of the center area. When the refractive index of the solid immersion lens 41 is designated n, the wavelength within the lens 41 becomes 1/n, and as a result the aperture number NA of the condenser lens 43 becomes a multiple of n. The spot size of the light beam LB is reduced to 1/n, and the resolution becomes a multiple of n. That is, when the aperture number NA of the condenser lens 43 is 0.5, the refractive index n of the solid immersion lens 41 is 1.8, and the wavelength xcex of the light beam LB is 780 nm, the spot size S is determined by equation (1) below; i.e., the spot size S is 430 nm.
S=xcex/(2 sin xcex8)xe2x80x83xe2x80x83(1)
In the hyperhemispherical solid immersion lens 42, the effective optical path is greater than the radius. In this instance, the spot size S of the light beam LB is determined by equation (2) below; i.e., the spot size S is 240 nm.
S=xcex/(2n sin xcex8)xe2x80x83xe2x80x83(2)
In this way, a condensed spot having a wavelength less than the used light can be obtained by using the solid immersion lenses 41 and 42. Using these methods, the spacing (air gap) b between the recording medium 44 and the solid immersion lens 41 and 42 must be sufficiently reduced so as to be maintained at approximately 100 nm or less. In order to control and maintain this air gap, it has been proposed to install the solid immersion lens on a floating slider applying the art of the magnetic hard disk. Prior art citations include U.S. Pat. Nos. 5,125,750, 5,774,281 and 5,786,947, and prior art citations using other than a floating slider include Japanese Laid-Open Application No. 8-212579.
The three issues below must be resolved to practicalize a high density memory using a solid immersion lens.
(1) Lens Holder Mechanism
In the conventional hemispherical and hyperhemispherical solid immersion lenses 41 and 42, it is difficult to prevent inclination (0 degree) of the plane surface 41b relative to the reference surface 49 of the support fixture 47 because there is no fixed reference to the support fixture 47 on the convex surface 41a, as shown in FIG. 16. When the plane surface 41b has a standard inclination, the fixed part of the lens disadvantageously protrudes to the object (medium) side of the lens, such that the required air gap cannot be ensured.
(2) Installation on the Slider
When installing a solid immersion lens on a floating slider for use as the recording head of a high density memory, the lens must be compact so as to have a diameter of 2 mm or less to reduce the head weight, and the lens support fixture must be provided with an air-bearing surface for floating. In this case, inclination between the support fixture and the lens plane surface must be prevented to maintain a sufficiently precise position of the solid immersion lens relative to the recording medium.
(3) Manufacturing Cost
Conventionally, hemispherical and hyperhemispherical solid immersion lenses are manufactured by grinding a glass member into a spherical shape to obtain a ball lens, then sectioning or grinding the ball lens. Such a production method, however, entails a complex process which raises the cost and is presently only in the experimental stage which does not result in a usable product.
An object of the present invention is to provide an improved solid immersion lens and production method thereof.
Another object of the present invention is to provide a solid immersion lens capable of being mounted so as to hold a predetermined position without inclination relative to a support fixture, and further capable of being mounted on a floating slider so as to sufficiently reduce the air gap with an object (medium).
Still another object of the present invention is to provide a production method capable of mass production of a solid immersion lens via a simple process at low cost.
These objects are attained by a first solid immersion lens of the present invention provided with a hemispherical shape or hyperhemispherical shape having a convex surface on the light entering side and an approximately plane surface on the light exiting side, wherein the convex surface comprises a positioning surface and a surface forming an effective optical path part. In this first solid immersion lens, it is desirable that the positioning surface is a curved surface having the opposite sign of the curvature of the surface forming the effective optical path part. Furthermore, includes a radius of curvature of infinity, i.e., a circular conical shape extending the tangent line of the radius at the effective optical path part.
A second solid immersion lens of the present invention provided with a hemispherical shape or hyperhemispherical shape having a convex surface on the light entering side and an approximately plane surface on the light exiting side, wherein a collar part having a positioning surface is provided outside the effective optical path part of the convex surface.
In the first and second solid immersion lenses, the positioning surface formed outside the effective optical path part of the convex surface comprises a fixed reference for the lens support fixture, and allows the solid immersion lens to be supported with excellent positioning (i.e., without inclination). Furthermore, the a sufficiently small air gap is ensured without the fixed part of the lens protruding on the object (medium) side.
Even when the lens is compact, the surface area of the approximate plane surface on the exit side is enlarged by providing the positioning surface, such that when the solid immersion lens is installed on a floating slider, the air-bearing surface is enlarged when floating. In addition to effectively preventing inclination, there is improved positioning accuracy of the solid immersion lens relative to the object (medium).
In the first solid immersion lens, the convex surface may comprise a first convex surface forming an effective optical path for forming a converged spot in the center of the approximate plane surface, and a second convex surface forming an effective optical path forming a converged spot at a location slightly separated from the approximate plane surface. In this way, a bifocal solid immersion lens can be obtained.
The first and second solid immersion lenses are manufactured by pressure molding a softened glass member using both a mold having a concave surface approximately inverting the convex shape, and a mold having a surface forming an approximate plane surface on the light exiting side. The pressure molding method using such molds allows inexpensive mass production of a solid immersion lens by a simple process which does not require cutting or grinding. If molten glass is dripped onto a mold having a surface for forming an approximate plane surface or having a concave surface approximately inverting the convex surface shape, the weight of the dripped glass can be evenly balanced so as to obtain a solaced immersion lens without dispersion.